Biomarker status conversion in locoregional breast cancer recurrence in a patient who had achieved pathologic complete response: a case report

Background: Breast cancer management has rapidly evolved over the past decade leading to successful pathologic complete response (pCR) in patients. Recurrence after pCR is uncommon but has been documented in the literature. Case Description: This report presents a rare case of locoregional breast cancer recurrence in a young 38-year-old woman with biomarker phenotype conversion from triple-negative breast cancer who had initially achieved pCR after nipple-sparing mastectomy and sentinel lymph node biopsy to human epidermal growth factor 2 (HER2) biomarker positive. In this report, we discuss biomarker phenotype conversion, including preanalytical and analytical variability, intratumor heterogenicity, and treatment options. Conclusions: We posit that performing simultaneous repeated receptor measurement and analysis on the original primary tumor specimen and the repeat biopsy may yield better results when discordance is suspected. Further, it is possible that local excision and axillary lymph node dissection followed by adjuvant therapy may provide a robust option to optimize progression-free survival. Medical therapies, including endocrine and chemotherapy, should be adjusted swiftly and accordingly in such cases. Finally, novel therapy options such as trastuzumab-deruxtecan may provide an additional approach for patients who continue to clinically progress despite prior targeted therapy. Through this case report, we aim to highlight the significance of proper tissue diagnosis and biomarker analysis in breast cancer recurrence.